1. Field of the Invention
The field of this invention is chemical emulsifying agents, or surfactants, and their use in asphalt emulsion technology.
2. Description of the Related Art
Properties of an asphalt emulsion depend greatly upon the chemical used as the emulsifier. An emulsifier is a surface-active agent that maintains the asphalt droplets of the asphalt emulsion in stable suspension and permits breaking at the proper time. The emulsifier does this by changing the surface tension at the area of contact between the asphalt droplet and the water in the emulsion.
Emulsifiers are classified in three categories, anionic, cationic, or nonionic. Among the most common anionic emulsifiers for asphalts are fatty acid wood product derivatives such as tall oils, rosins, and lignins. These anionic emulsifiers are most typically saponified through a reaction with potassium hydroxide or sodium hydroxide.
The most common cationic emulsifiers are fatty amines such as diamines, imidazolines, and amidoamines, and fatty quaternary ammonium salts The fatty amines are saponified through reaction with an acid, most typically hydrochloric. Fatty quaternary ammonium salts are stable, water-soluble salts that make effective cationic emulsifiers.
A long-felt need has existed among those schooled in the art of asphaltic mixing grade emulsions to control the mixability of the mixing grade emulsion/aggregate mixture to both mix for long periods of time and the emulsion still have the ability to break, and/or set, or otherwise create a bond between the ruptured or rupturing asphalt droplet of the emulsion and the aggregate within a short period of time under laboratory conditions. It is desired to have a mix time greater than five (5) minutes while retaining the emulsion's bond, break, and/or setability to within thirty (30) minutes. It is also desirous to be able to correct or adjust the emulsion formulation to accommodate variations in operational conditions. Examples of these variations include aggregate type, aggregate gradation, aggregate moisture, aggregate adsorption, total moisture in the emulsion/aggregate mixture, and actual field conditions. Those schooled in the art of asphaltic mixing grade emulsions could traditionally control the above-described parameters by decreasing aggregate moisture, total moisture, or other similar adjustments to the aggregate portion of the emulsion/aggregate mixture. If adjustment to the aggregate portion was not practical, then adjustments to the emulsifier and/or emulsifiers, used in making the emulsion were attempted. These attempts to adjust the emulsion/aggregate mixture through the emulsifier portion of the emulsion will generally create problems such as the inability of the emulsion/aggregate mixture to mix for five (5) minutes and/or slow break and/or set times (greater than thirty minutes).
The technique of adjusting the emulsifier portion may incorporate the use of non-ionic emulsifiers which contain no functional end group on the molecule of the chemical used. A further technique is to use other combinations of chemicals known in the asphalt emulsion industry to improve the mixability of the emulsion/aggregate mixture. Examples of chemicals known in the industry to improve the mixability of the emulsion/aggregate mixture include but are not limited to: primary amines and/or hydrocarbon oxides thereof; secondary amines and/or hydrocarbon oxides thereof; tertiary amines and/or hydrocarbon oxides thereof; quaternary amines and/or hydrocarbon oxides thereof; amido amines and/or hydrocarbon oxides thereof; imidazolines and/or hydrocarbon oxides thereof; sulfates and/or hydrocarbon oxides thereof; sulfites and/or hydrocarbon oxides thereof; carboxylic acids and/or the like and/or hydrocarbon oxides thereof; ethoxylated and/or propoxylated (and/or the like and/or similar hydrocarbon oxides) and/or other similar or like chemical moieties and/or variations; and/or mixtures of any or all the above thereof.
The use of these chemicals may be helpful in improving one particular parameter in the emulsion/aggregate mixture, but will adversely affect other parameters. An example of this is the common use of nonylphenol ethoxylates that have high molar quantities (&gt;50 and typically 100 moles) of ethylene oxide reacted with the nonylphenol to form this chemical family that is used as the primary emulsifier in the emulsion portion of the mix. Nonylphenol ethoxylates (and in particular those described above) will improve the mixability but will adversely affect the break and/or set time (normally excessively lengthened), as well as the cure or adhesion to the aggregate portion of the emulsion/aggregate mixture.
Another technique used to control or improve the mixability and/or break and/or set time of the emulsion/aggregate mixture is to decrease the amount of moisture present in the aggregate to less than one percent (1%) by weight of aggregate and add petroleum distillates (naphtha, kerosene, diesel, and the like) either singularly or in various combinations to the emulsion formulation. Petroleum distillates will not normally tolerate aggregate moisture contents above one percent (1%) by weight of aggregate while still allowing for mixing and one hundred percent (100%) coating of the aggregate by the emulsion during the emulsion/aggregate mixing portion of the overall operation. The inability of the emulsion containing petroleum distillates to mix at ambient temperatures with aggregates with a moisture content typically greater than two percent (2%) by weight of aggregate is of great commercial significance. The inability of the emulsion containing petroleum distillates, sometimes referred to as "cutback" emulsions, to mix with aggregates of higher moisture content creates the necessary and costly step of drying the aggregate to typically less than one percent (1%) by weight of water before coating or mixing of the emulsion will occur. Further, the distillate content of the emulsion formula is generally above six percent (6%) by weight of total emulsion and is usually between eight and fifteen percent (8 and 15%) by weight of total emulsion. Petroleum distillates can, and often do, place the emulsion mixing grade products in an economically disadvantaged position with other products in the marketplace, such as cutback asphalt, hot mix, and other type products.
The particular problem of adding petroleum distillates to the emulsion formulation also creates specific problems related to the petroleum distillate's effect on the physical properties of the emulsion residue from distillation. Examples of such physical properties of the emulsion residue from distillation adversely affected by the addition of petroleum distillates to the emulsion formulation are:
1. high penetration values;
2. low absolute viscosity values;
3. low ring and ball softening point values.
Previous to the invention disclosed herein, it was not practical, and in some cases impossible, to control the above-described relationships of the emulsion/aggregate mixture. Further, it was also difficult (and in some cases impossible) to control the above-described relationships of the emulsion residue from distillation properties due to the undesirable effects of the emulsifier and the use of petroleum distillates used as part of the emulsion formulation when making the mixing grade emulsion portion of the emulsion/aggregate mix.